<p>This is an embed:</p>
<iframe class="embed" src="https://www.youtube.com/watch?v=dQw4w9WgXcQ"></iframe>
<p>So is this, with only three spaces of indentation:</p>
<iframe class="embed" src="https://www.youtube.com/watch?v=dQw4w9WgXcQ"></iframe>
<p>This is not, because it's fully indented:</p>
<pre><code>https://www.youtube.com/watch?v=dQw4w9WgXcQ
</code></pre>
<p>This is not, because it has extra bits after the URL:</p>
<p><a href="https://www.youtube.com/watch?v=dQw4w9WgXcQ">https://www.youtube.com/watch?v=dQw4w9WgXcQ</a> &lt;-- you gotta watch this!</p>
<p>This is not, because it's in a fenced code block:</p>
<pre><code class="language-md">
https://www.youtube.com/watch?v=dQw4w9WgXcQ

</code></pre>
<p>And this isn't either because it's inline: <img src="https://www.youtube.com/watch?v=dQw4w9WgXcQ" alt="" /></p>
<p>Embeds can't be nested in other blocks:</p>
<ul>
<li>https://www.youtube.com/watch?v=dQw4w9WgXcQ
<ul>
<li>https://www.youtube.com/watch?v=dQw4w9WgXcQ</li>
</ul>
</li>
</ul>
<p>This isn't valid because it's a lazy paragraph continuation:
<a href="https://www.youtube.com/watch?v=dQw4w9WgXcQ">https://www.youtube.com/watch?v=dQw4w9WgXcQ</a></p>
<iframe class="embed" src="https://www.youtube.com/watch?v=dQw4w9WgXcQ"></iframe>
<p>^ This is fine, though</p>
